Police in Washington are investigating an incident in which the host of Meet the Press displayed what he described as a high-capacity ammunition magazine.

While interviewing Wayne LaPierre, chief executive of the National Rifle Association, on the NBC programme, David Gregory held an object, apparently as a prop to make a point, and said it was a magazine that could hold 30 rounds.

"Here is a magazine for ammunition that carries 30 bullets. Now, isn't it possible if we got rid of these, if we replaced them and said: 'Well, you can only have a magazine that carries five bullets or 10 bullets,' isn't it just possible that we could reduce the carnage in a situation like Newtown?" Gregory asked, referring to the recent mass shooting at an elementary school in Connecticut.

High-capacity ammunition magazines are banned in the capital district, regardless of whether they are attached to a firearm. Meet the Press is generally taped in Washington.

A police spokeswoman said the department was investigating whether Gregory may have violated city firearms laws. She declined to comment further. An email seeking comment from NBC was not immediately returned.